1. A high-molecular-weight renin ( M r 60 000) was formed by the reaction of a low-molecular-weight renin ( M r 40 000) with a renin-binding substance in canine renal cortical extract in the presence of the sulphydryl (SH) group oxidizing agent potassium tetrathionate; thus the reaction required SH oxidation. 2. Renin extracted from isolated renin granules was adsorbed on to thiopropyl Sepharose 6B, and then liberated with dithiothreitol (50 mmol/l), indicating that it possessed on SH moiety(s). 3. However, the renin was capable of reaction with the renin-binding substance even after its SH moiety (or moieties) was protected with 5,5′-dithiobis-(2-nitrobenzoic acid). 4. The high-molecular-weight renin was converted into the low-molecular-weight renin by incubation (37°C, 15 min) with cytosol (soluble fraction) of renal cortex and liver. Such converting ability was diminished after the cytosol was treated with perchloric acid or potassium tetrathionate. 5. These results suggest that the reaction of renin with the renin-binding substance does not require disulphide bond(s) and that an enzymelike substance which is sensitive to SH oxidation is involved in the conversion from the high-molecular-weight renin into the low-molecular weight renin.

1. The low-molecular-weight (40 000) form of renin was converted into the high-molecular-weight (60 000) form of renin with sulphydryl oxidation, and the high-molecular-weight form of renin was re-converted into the low-molecular-weight form with a reduction of disulphide bonds in the renal cortical homogenate of the dog. Therefore, the low- and high-molecular-weight forms of renin were interconvertible. 2. The formation of high-molecular-weight form of renin required a renin binding substance which was found to be included in the cytosol fraction of kidney cortex of the dog. 3. The renin binding substance of the dog was unstable to heat and low pH, but vitally resistant to Triton X-100 and chloroform. It did not bind to concanavalin A Sepharose 4B. 4. The renin binding substance was eluted in the molecular-weight region between 156 000 and 60 000 on Sephadex G-200, and such apparent molecular weight was not altered by urea at 4 mol/l; thus molecular weight greater than the theoretically expected value of 20 000 was indicated.

1. Blood lead and erythrocyte glutathione reductase (GSSG-R) and glucose 6-phosphate dehydrogenase (G6P-D) activities were measured in normal subjects and in those with occupational exposure to lead. 2. With increasing blood lead concentration, GSSG-R activity increases and that of G6P-D decreases. 3. It is suggested that these changes represent part of a compensatory mechanism to overcome the reduction of sulphydryl groups by lead ions.